1. CHEM 120 WEEK 13 LECTURES (INORGANIC WEEK 4) Dr. MD BALA

2. The Ostwald Process – manufacture of HNO 3 Nitrogen Contd…

3. Reactions and uses of HNO 3 : -is a strong oxidizing agent (due to the NO 3 - ion) - it oxidizes and dissolves most metals. A 33 % HNO 3, HCl 66 % mixture is called aqua regia and is used to dissolve gold bearing ores (gold mining in SA and elsewhere) - spent fuel rods (nuclear power stations) contain about 35 metals. These metals are recovered by dissolving the rods in HNO 3 conc. HNO 3 gives NO 2 (g) as a by-product dilute HNO 3 gives NO (g) as a by-product Cu 2+ (aq) NO 2 (g)

4. also used in the manufacture of explosives, e.g. nitroglycerine, nitrocellulose, trinitrotoluene (TNT) Dynamite Decomposition of TNT 2 C 7 H 5 N 3 O 6 → 3 N 2 + 5 H 2 O + 7 CO + 7 C Trinitrotoluene (TNT) is 2,4,6- trinitromethyl benzene

5. The Haber-Bosch Process (manufacture of NH 3 ) Compressor catalyst unreacted N 2 and H 2 condenser NH 3 (l) N 2 (g) + 3H 2 (g) Reactor 400 O C, 200 atm Storage continuous removal of NH 3 recycling 100 % yield e.g. iron oxide N 2 (g) + 3H 2 (g) ⇌ 2NH 3 (g)

6. Sulfur Sulfur crystals Pyrite- iron disulfide (FeS 2 )

7. The Frasch process 3 concentric pipes (160 0 C and 16 atm) (20 – 25 atm) Method of extracting sulfur from underground deposits

8. Reactions and uses of SO 2 :

9. colourless S + ) The Contact Process: Industrial production of H 2 SO 4 Physical descriptions: SO 3 : white solid, low bp. (45 °C), volatile H 2 SO 4 : dense, colourless oily liquid.

10. Exercise: The Contact Process 1.What is the oxidation number of S in the first reaction of the contact process 2.What is being reduced in the second reaction? 3.H 2 S 2 O 7 is known as oleum. What is the oxidation state of S in this compound?

11. Reactions of H 2 SO 4 : Conc. H 2 SO 4 has a strong affinity for water dehydrating C 12 H 22 O 11 (s) conc. H2SO4 12C (s) + 11H 2 O (l) sugar Dilute H 2 SO 4 : - reacts with metals to produce H 2 (g) - dissolves carbonates and produces CO 2 (g)

12. SO 2 emissions and the environment Industrial smog is made up of SO 2, NO, H 2 SO 4 mist and particulate matter (ash and smoke) Mainly produced by industries (fuel producers, power plants burning coal for energy)

13. SO 2 monitoring in Durban and surrounding areas http://www2.nilu.no/AirQuality/data/reports/%7B4D6B87DA-BCDC-BAD1-AD0A-B8BEBC90A261%7D.pdf

14. SO 2 monitoring trends in Durban from 2004 to 2007 http://www2.nilu.no/AirQuality/data/reports/%7B04C989F2-BCDC-BAD1-AB14-6F89EE7A9364%7D.pdf

15. SO 2 (g) + NO 2 (g) SO 3 (g) + NO (g) SO 3 (g) + H 2 O (l) H 2 SO 4 (component of acid rain) Acid Rain is caused by a combination of SO 2 and oxides of nitrogen, such as NO 2, with rain water in the atmosphere acid rain damages buildings, chemically burns the leaves of plants, destroys forests and poisons lake water. it lowers the pH of lake waters resulting in death of aquatic life

16. Phosphoric Acid P 4 O 10 (s) + 6H 2 O (l) 4H 3 PO 4 (aq) Tetraphosphorus decaoxide phosphoric acid normally only get 87.3 % of pure H 3 PO 4 (orthophosphoric acid) missing amount is present as H 4 P 2 O 7 (diphosphoric acid) produced when water is lost from between 2 orthophosphoric acid molecules

17. Phosphoric acid present in living organisms adenosine diphosphate adenosine triphosphate

19. Phosphates as fertilizers Fertilizer production involves the mining of phosphate rock, e.g., fluoroapatite, Ca 3 (PO 4 )2.CaF 2 (Note: this poses a fluoride waste problem) Ca 3 (PO 4 ) 2 has a low solubility poor uptake by plant react it with H 2 SO 4 to form (soluble) superphosphate and gypsum Ca 3 (PO 4 ) 2 (s) + 2H 2 SO 4(aq) Ca(H 2 PO 4 ) 2 (s) + 2CaSO 4(s) superphosphategypsum

20. excess fertilizer use can lead to phosphate pollution of lakes, ponds and streams leading to eutrophication (explosion of plant growth especially algae) algae cause depletion of oxygen which leads to death of fish and aquatic life

21. Peroxide Chemistry A peroxide has the general formula of M 2 O 2 -contains O – O bond where oxygen has an oxidation state of – 1 8 e - 14 e - 13 e -

22. (most active) K, Rb, CsNa, Ca, Sr, Baless active metals KO 2, RbO 2, CsO 2 Na 2 O 2, Ca 2 O 2, normal oxides (superoxides) Sr 2 O 2, Ba 2 O 2 (peroxides) O2O2 KO 2 – used as a source of O 2 in masks used for rescue work Na 2 O 2 – bleaching agent Na 2 O 2, Li 2 O 2 – used in emergency breathing devices 2Li 2 O 2 (s) + 2CO 2 (g) 2LiCO 3 (s)+ O 2 (g)

23. Base: H 2 O 2 (aq) + 2e - 2OH - (aq) Acid: H 2 O 2 (aq) + 2e - +2H + 2H 2 O(l) the oxides, peroxides and superoxides all react with water to from basic solutions Most well known peroxide is hydrogen peroxide O 2 2- (aq) + 2H 2 O (l) 2OH - (aq) + H 2 O 2 (aq) slow decomposition 2H 2 O 2 (l) 2H 2 O (l) + O 2 (g)

24. Exercise Write balanced equations for the following oxidation reactions using H 2 O 2 : a) SO 3 2- to SO 4 2- in acid b) Mn 2+ to MnO 2 in base

25. The Diaphragm Chlor-alkali Process 2Cl - (aq) + 2H 2 O(l) 2OH - (aq) +H 2 (g) + Cl 2 (g) Cl disproportionates into ClO - (aq), ClO 3 - (aq) and Cl - (aq) if it comes into contact with NaOH NaCl level is kept higher to allow for the slow release of NaCl into the cathode compartment prevents backflow of NaOH

26. The Mercury-cell Chlor-alkali Process Produces a higher purity of NaOH Hg cathode cathode Reduction of H 2 O to H 2 (g) and OH - (aq) requires a high potential Instead Na + (aq) gets reduced to Na (in Hg) and Cl 2 (g) forms 2Na + (aq) + 2Cl - (aq) 2Na(in Hg) + Cl 2 (g)E 0 cell = -3.20V 2Na(in Hg) + H 2 O(l) 2NaOH(aq) + H 2 (g) + Hg(l)

27. Manufacture of HCl HCl Synthesis Unit Demineralized Water HCl Storage Tank HCl Product H 2 Feed Cl 2 Feed Tail Gas Scrubber Vent Combustion http://www.akersolutions.com/Internet/IndustriesAndServices/Process/IndustrialChemicals/ HydrochloricAcidProcess.htm (absorbs most of the HCl gas) Tail gas scrubber removes residual acid vapour before most of the non-condensable gas is vented to the atmosphere H 2 and Cl 2 comes from the Chlor-alkali process

28. Products of the Chlor-alkali industry